Receiving system



May 15, 1962 A. G. MANKE ETAL RECEIVING SYSTEM original Filed Nov.'4,195e ATTORNE Y 5,@ KD NO AH MR Glu. RR U0 HI Tw MJ w, .m24 mi N UnitedStates Patent O 7 Claims. (Cl. Z50-20) The present invention relates toreceiving systems and has as an object thereof to provide an improvedmeans for receiving a plurality of signals. The present applicationcomprises a continuation of copending application Serial No. 544,935,filed November 4, 1955, now abandonded.

Another object of the present invention is `to provide improved meansfor simultaneously monitoring a plurality of carrier modulated Wavechannels.

ln carrying out the present invention, in one form, there is provided apair of converter devices, each including a pair of input circuits and acommon output circuit. One input circuit of each of the converterdevices is responsive to one of a pair of carrier modulated waves eachhaving a different carrier frequency. To the other input circuit of oneof said converter devices is applied a wave having a frequency differingon the low side from the carrier frequency of one of said Waves by apredetermined value. To the other input circuit of the other of saidconverter devices is applied a wave having a frequency higher than thehigher of the carrier frequencies of said two carrier waves by saidpredetermined value. Thus, the output of each of the converter devicesis a modulated carrier wave having the same carrier frequency.

Novel features which are believed to be characteristic of this inventionare set forth in particularity in the appended claims. The inventionitself, however, both as to its organization and method of operation,together with further objects and advantages thereof, may best beunderstood by reference to the following description taken in connectionwith the accompanying drawings in which is shown an illustrativeembodiment of the present invention, partially in schematic as appliedto a frequency modulated receiver.

Referring now to the single gure of the drawing, there is shown anillustrative embodiment of a receiver system embodying the presentinvention. This system includes an antenna 1 for receiving frequencymodulated carrier waves and a radio frequency amplifier 2 forarnplifying the received frequency modulated carrier waves lying in aparticular band of frequencies. The output from the radio frequencyamplier 2 is coupled to first converter 3 and second converter 4. Localoscillators 5 and 6 function in conjunction with the converters 3 and 4,respectively. The output from the converters 3 and 4 are coupled to highintermediate frequency amplifier 7. The receiver additionally includes asecond converter 8, a second local oscillator 9, a low intermediatefrequency amplifier 10, a first limiter 11, a second limiter 12, adiscriminator 13 and an audio channel 14, the latter recited elementsbeing entirely conventional in frequency modulated receivers.

Referring now particularly to the schematic portion of the drawing,first converter 3 comprises an electron discharge device 15, including acathode 16, a grid 17, a screen grid 18, suppressor grid 19 and an anode20. Second converter 4 comprises an electron discharge device 21,including a cathode 22, a grid 23, a screen grid 24, a suppressor grid25 and an anode 26. Cathode 16 of electron discharge device 15 isconnected through bias resistance 27 bypassed by by-pass capacitor 28and ICC through degenerative coupling resistance 29 and switch 62 toground. Grid 17 is connected through coupling capacitor 30 to one sideof tuned circuit 31, the other side of which is connected to ground.Grid 17 is also connected through grid resistance 32 to ground. Screengrid 18 is connected through screen load resistance 33 to the positiveterminal of source of operating potential 34, the negative terminal ofwhich is connected to ground. Screen grid 18 is also connected to groundthrough bypass capacitor 35. The suppressor grid 19 is connected toground. The anode 20 is connected through the primary winding of tunedtransformer 36 to the positive terminal of source 34. The primarywinding of tuned transformer 36 is tuned by capacitance 37 connected inshunt therewith. The secondary winding of tuned transformer 36 isshunted by tuning capacitor 38. One end of the secondary winding oftuned transformer 36 is connected to ground, the other end iscapacitively coupled through capacitor 39 to the input of the highintermediate frequency amplifier 7.

Cathode 22 of electron discharge device 21 is connected through cathodebias resistance 40 bypassed by by-pass capacitor 41 through degenerativecoupling resistance 42, and switch 62 to ground. The grid 23 isconnected through coupling capacitor 43 to the ungrounded side of thetuned circuit 31. The grid 23 is also connected through grid resistance44 to ground. The screen 24 is connected through screen load resistance45 to the positive terminal of the source of Voperating potential 34.The screen 24 is also connected through screen by-pass capacitor 46 ltoground. The suppressor grid 25 is connected to ground. The anode 26 isconnected to the anode 20. Converter 3 and converter 4 are supplied withsignals received from the radio frequency amplifier 2 via tuned circuit31 and respectively grid 17 of electron discharge device 15 and grid 23of electron discharge device 21.

The cathode circuits of converters 3 and 4 are supplied with localoscillations from local oscillators 5 and 6, respectively. Localoscillator 5 comprises an electron discharge device `48, including acathode `49, a grid 50 and an anode 51. The cathode 49 is connected tothe junction of resistances 27 and 29. The grid 50 is connected throughpiezoelectric device 52, by-passed by grid leak resistance 53 to ground.The piezoelectric device is arranged -to preferably operate on aharmonic of its fundamental mode of oscillation for simplifying theapparatus necessary to develop the desired higher frequency usuallynecessary in radio communication converter arrangements. The anode 51 isconnected through tuned circuit 54 to positive terminal of source ofoperating potential 34.

The local oscillator 6 comprises an electron discharge device 55,including a cathode 56, ya grid 57 and an anode 58. The cathode 56 isconnected to the junction of resistances 40 and 42. The grid 57 isconnected through piezoelectric device 59, by-passed by grid leakresistance 60 to ground. The `anode 58 is connected through tunedcircuit 61 to the positive terminal of source 34.

Resistances 29 and 42 are connected to ground through switch device 62which includes a terminal 63 connected to one end of resistance 29, aterminal 64 connected to the corresponding end of resistance 42, and aterminal 65 connected to ground. Switch 62 includes a shorting member 66which in one position shorts the contacts 63, 64 and 65 togethergrounding the ends of resistances 29 and 42. In another position,shotting bar 66 is permitted to ground only terminals 63 to 65, thus ineffect rendering converter 4 inoperative. Also, with the shorting member66 in the extreme right position, contact is made between terminals 64and 65, thereby disconnecting the converter 3 from circuit and renderingit inoperative.

The present invention is particularly useful for simultaneouslymonitoring two frequency modulated carrier wave channels at adjacentcarrier frequencies. 'Ihe two carrier frequencies are spaced such thatthe tuned circuits of the R-F amplier 2 are able to pass received waves4on to the converters and 4. The switch 62 is maintained in a positionsuch that both converters 3 and 4 are operating. Waves appearing in theoutput circuit of the R-F amplifier 2 from antenna 1 are applied viatuned circuit 31 to the grid input circuits of converters 3 and 4. Thefrequency ofthe wave developed by local oscillator 5 is arranged to belower in frequency than the lower of the two carrier frequencies by apredetermined dierence in frequency. Similarly, the frequency of theoutput of the local oscillator 6 is arranged to be higher than thehigher of the two carrier frequencies by the same predetermineddilference in frequency. The application of these waves to converters 3Yand 4, respectively, cause the appearance in the common output circuitof the converters of the two carrier modulated waves each having acarrier frequency equal to the predetermined difference frequency. Thetuned circuit in the output of the converters 3 and 4 comprising theprimary winding of transformer 36 and the capacitance 37 is tuned tothis difference frequency. Accordingly, it is seen that in this outputcircuit two frequency modulated carrier waves having carrier frequenciesadjacent to one another are converted in effect to two other waves ofthe same but lower carrier frequency. Thus the two frequencies can bemonitored simultaneously.

An advantage of the arrangement of having the local oscillatorfrequencies lie outside of the range including the carrier frequenciesof the applied frequency modulated signals is that cross-modulation andother undesirable interfering effects in the converters aresubstantially avoided.

In the arrangement of the present invention of coupling the localoscillator waves into the cathode circuits of the converters while theincoming carrier modulated waves are applied to the grids of theconverter devices 3 and 4, cross-modulation and loading effects of oneoscillator on the other are substantially eliminated, inasmuch as thegrid-cathode capacitance of one of the converter devices effectivelyaffords a high impedance to currents passing to the other localoscillator device. Further isolation of the two oscillators can beobtained by injecting voltage from each of the 'oscillators 5 and 6 ontothe suppressor grid of respective electron discharge devices and 21.Also the waves from each of oscillators 5 and 6 could be applied to thescreen grid of electron discharge devices 15 and 21, respectively, or toa suppressor grid of one electrony discharge'device and a screen grid ofthe other electron discharge device. ln s-uch a case, it will beunderstood that the cathode resistances may be by-passed. It will alsobe understood that three electrode electron discharge devices as well asfive electrode electron discharge devices may be used for the converterfunction. Also, semiconductor type translating devices may as well beused for this purpose.

iAnother advantage of applicants arrangement is that by the use ofunbypassed resistances 29 and 42 in the cathode circuits of theconverters 3 and 4, respectively, for the coupling function, sufcientdegeneration is introduced into the converter circuits therebyminimizing loading of the input circuits of the converter devices andconsequent tuning thereof.

Should it be desired to receive or monitor more Vthan two frequencies,this can be accomplished by injecting local oscillations as shown and,in addition, injecting a third conversion frequency onto the suppressorgrid of one of the electron discharge devices 15 and 21.

While there has been shown a particular embodiment of the invention, itwill, of course, be understood that it is not limited thereto since manymodifications both in circuit arrangement and in the instrumentalitiesemployed 4 t pended claims to cover any such modifications that comewithin the true spirit and scope of our invention.

What we claim as new and desired to secure by Letters Patent of theUnited States is:

1. In combination, in an FM radio receiver, a pair of frequencyconverters, each including a pair of input circuits and an outputcircuit, means for applying carrier waves of different carrierfrequencies to an input circuit of each of said converters, means'forapplying to the other input circuit of one of said converters a wavehaving a frequency below the lower in equency of said carrier waves by apredetermined value, means for applying to the other of said convertersa wave having a frequency above vthe higher in frequency of said carrierwaves by said predetermined value, means for deriving from the outputcircuit of said converters carrier waves having the same carrierfrequency, and means including a limiter responsive to only thesubstantially stronger of said derived waves from both of saidconverters when carrier waves of the two different carrier frequenciesare received simultaneously.

2. In combination, in an PM radio receiver, a pair of frequencyconverters each including an input electrode, an output electrode, andVa common electrode, means for applying modulated carrier waves ofdifferent frequencies lbetween each of said input electrodes and apredetermined potential point, means for applying between one of saidcommon electrodes `and said predetermined potential point a wave havinga frequency below the lower in frequency of said carrier waves by apredetermined frequency, means for applying :between the other of saidcommon electrodes and said predetermined potential point a wave having afrequency above the higher in frequency of said carrier waves by saidpredetermined frequency, an output circuit connected between each ofsaid output electrodes and said predetermined potential point forderiving from said devices modulated carrier waves having a carrierfrequency equal to said dierence in frequency, and means including a`limiter coupled to said output circuit responsive only to thesubstantially stronger signal from said pair of frequency converterswhen said modulated carrier waves of different frequencies are appliedsimultaneously.

3. In combination, in an FM radio receiver, a pair of frequencyconverters, each including an input electrode, an output electrode, anda common electrode, means for applying carrier waves of differentfrequencies between may be made and it is, therefore, contemplated bythe apeach of said input electrodes and ground, an unbypassed resistiveelement connected between one of said common electrodes and ground,means for applying across said resistive element a wave having afrequency below the lower frequency of said carrier waves by apredetermined frequency, another unbypassed resistive element connected:between the other of said common electrodes and ground, means forapplying a wave having a frequency above the higher in frequency of saidcarrier waves -by said predetermined frequency across said otherresistive element, `an output circuit connected between each of saidoutput electrodes and ground for deriving from said devices carrierwaves having the same carrier frequencies, and means including a limitercoupled to said output circuit responsive only to the substantiallystronger signal from said pair of frequency converters when saidmodulated carrier waves of different frequencies are appliedsimultaneously.

4. In combination, in an FM radio receiver, a pair of electron dischargedevices, each including a cathode, a grid and an anode, means forcoupling carrier waves of dierent frequencies between each of said gridsand ground, a pair of unbypassed resistances each connected between arespective cathode `and ground, means for applying across one of saidresistances a wave having a frequency below the lower in frequency ofsaid carrier waves by a predetermined difference in frequency, means forapplying across the other of said resistances a wave having a frequencyabove the higher in frequency of said carrier waves by saidpredetermined difference, an output circuit tuned to said difference infrequency connected between each of said anodes and ground for derivingfrom said devices carrier waves having the same frequencies forconverting said carrier waves of different waves to carrier waves of thesame frequency, and means including a limiter coupled to said outputcircuits and responsive only to the substantially stronger of saidcarrier Waves of different frequencies when said carrier waves ofdierent frequencies are received simultaneously.

5. In a radio receiving system for receiving frequency modulated waves,including a converter having a pair of input circuits and an outputcircuit to one input circuit of which is applied a iirst modulatedcarrier wave and to the other input circuit of which is applied a wavehaving a frequency differing from the carrier frequency of said firstmodulated carrier wave by a predetermined frequency, yand from .theoutput circuit of which is obtained a second modulated carrier wavehaving a carrier frequency equal to said difference in frequency, 4thecombination including another converter, including a pair of inputcircuits and an output circuit, one of said input circuits being coupledto the input circuit of said one converter, the output circuit of saidother converter being coupled to the output circuit of said oneconverter, means for applying to the other input circuit of said otherconverter a Wave having a frequency differing from the frequency of athird modulated carrier wave applied to the input circuits of saidconverter by said predetermined difference in frequency, said frequencyof said other wave being arranged such that said two carrier frequencieslie between said two applied converting frequencies, and means includinga limiter responsive only to the substantially stronger of the signalsfrom said output circuits when waves of said two carrier Afrequenciesare received simultaneously.

6. FM receiving apparatus for simultaneously monitoring a pair offrequencies comprising rst and second frequency converters, a firstlocal oscillator developing a signal having a frequency which is lowerthan the lower` of said pair of frequencies .by a predeterminedfrequency, a second local oscillator developing signal having afrequency which is higher than the higher of said pair of frequencies bysaid predetermined frequency, said first frequency converter beingresponsive to la received signal at the lower of said pair offrequencies and to the signal from said first local `oscillator todevelop an output signal at said predetermined frequency, said secondfrequency converter being responsive to a received signal at the higherof said pair of frequencies and to the signal from said Isecond localoscillator to develop an output signal at said predetermined frequency,and limiting means responsive only to the substantially stronger outputsignals of said rst and second frequency converters when signals `ofsaid pair of frequencies are received simultaneously.

7. -FM receiving apparatus comprising first means responsive to :afrequency-modulated signal of a first frequency for producing afrequency-modulated signal of a second frequency, second meansresponsive to a frequency-modulated `signal of a third frequencydifferent than said rst Ifrequency for producing a frequencymodulatedsignal of said second frequency, and means including limiting meansresponsive to frequency-modulated signals of said second frequency and,when frequency-modulated signals of said first and third frequencies arepresent simultaneously, responsive only to the substantially stronger ofsaid frequency-modulated signals of said first and third frequencies.

References Cited in the tile of this patent UNITED STATES PATENTS1,746,446 Shapiro Feb. ll, 1930 1,968,099 Shumard July 31, 19342,108,088 Tufts Feb. 15, 1938 2,266,670 Winfield Dec. 16, 1941 2,664,501Whidden Dec. 29, 1953

